1. Field of the Invention
The present invention relates to a radio transceiver station, a radio communication system for an industrial automation system, and a method for operating the radio communication syste.
2. Detailed Description of the Related Art
Industrial automation systems are used to monitor, control and regulate technical processes, particularly in the field of manufacturing, process and building automation, and make it possible to operate control devices, sensors, machines and industrial installations in a manner that is intended to be as independent as possible and independent of human interventions. On account of a constantly increasing importance of information technology for automation systems comprising numerous networked control or computer units, methods for reliably providing functions distributed across an automation system for providing monitoring, control and regulation functions are becoming increasingly important.
Interruptions in communication connections between computer units of an industrial automation system or automation devices may result in undesirable or unnecessary repetition of the transmission of a service request. This causes additional utilization of communication connections of the industrial automation system, which may result in further system faults or errors. In addition, untransmitted messages or incompletely transmitted messages may prevent an industrial automation system from changing to or remaining in a safe operating state, for example. This may finally result in failure of an entire production installation and costly production downtime. A particular problem regularly results in industrial automation systems from message traffic with a comparatively large number of, but relatively short, messages, thus intensifying the above problems.
In order to be able to compensate for failures of communication connections or devices, communication protocols, such as Media Redundancy Protocol, High-availability Seamless Redundancy or Parallel Redundancy Protocol, have been developed for highly available industrial communication networks that can be operated in a redundant manner. The Media Redundancy Protocol (MSR) is defined in the International Electrotechnical Commission (IEC) 62439 standard and makes it possible to compensate for individual connection failures in networks having a simple ring topology in the case of bumpy redundant transmission of messages. According to the Media Redundancy Protocol, a redundancy manager is assigned to a switch having two ports inside the ring topology, where the redundancy manager monitors the network for connection failures and possibly initiates a switching measure to close the ring.
Bumpy media redundancy methods can be implemented, in principle, with relatively little effort. However, the disadvantage is that, on the one hand, messages may be lost in the event of a fault and, on the other hand, a fault state is first of all present during reconfiguration of a communication network. Such a fault state must be safeguarded via a superimposed communication protocol, for example using TCP/IP on the network or transport layer, in order to avoid an interruption in a communication connection.
PROFINET (IEC 61158 Type 10) also refers to the Media Redundancy Protocol as a bumpy media redundancy method inside a communication network with a ring topology. In contrast, Media Redundancy Planned Duplication (MRPD) is an extension for bumpless transmission of isochronous real-time data. However, Media Redundancy Planned Duplication is not an application-neutral bumpless media redundancy method but rather a PROFINET-specific extension.
High-availability Seamless Redundancy (HSR) and the Parallel Redundancy Protocol (PRP) are defined in the IEC 62439-3 standard and make it possible to bumplessly transmit messages in a redundant manner with extremely short recovery times. According to High-availability Seamless Redundancy and the Parallel Redundancy Protocol, each message is duplicated by a transmitting communication device and is sent to a receiver on two different paths. A communication device at the receiver end filters redundant messages constituting duplicates from a received data stream.
The IEC 62439-3 standard has previously prescribed exclusively wired transmission paths for the Parallel Redundancy Protocol (PRP) on account of relatively long latency delays in wireless communication systems and a non-deterministic transmission behavior caused thereby. Suitability of WLAN transmission paths in PRP communication networks is investigated in “Towards a Reliable Parallel Redundant WLAN Black Channel”, Markus Rentschler, Per Laukemann, IEEE 2012. Parallel application of various diversity techniques for space, time and frequency, for example, can be used to compensate adequately for effects of stochastic channel fading in WLAN communication networks.
EP 2 712 124 A1 discloses a redundantly operated industrial communication system having communication devices redundantly connected to an industrial communication network, in which messages are transmitted wirelessly at least in sections. A plurality of buffer storage units for message elements received in a wired manner at a network node and for message elements to be wirelessly transmitted by the latter are provided in the industrial communication network. If a maximum buffer size is exceeded, an oldest message element in the respective buffer storage unit is deleted. Until the maximum buffer size is exceeded, the oldest message element is selected as the next message element to be wirelessly transmitted.
DE 10 2012 209509 A1 describes an apparatus for securely transmitting data between a mobile subscriber having at least one transmission apparatus and a stationary receiver. Here, the mobile subscriber can change between a plurality of radio cells. Each radio cell has at least one transmission apparatus that is connected to at least one network in a wired manner. The stationary receiver is likewise connected to the at least one network in a wired manner. Both the wireless transmission between the mobile subscriber and the respectively associated transmission apparatus and the wired transmission of data between the transmission apparatus and the at least one associated network are performed in a redundant manner. The stationary receiver is connected to the network in a redundant and wired manner.
In order to connect automation devices having completely independent Ethernet interfaces within a redundant communication network to singly connected automation devices in a highly available manner, a Y switch is used for the respective singly connected automation device as disclosed in DE 10 2013 211406 A1. Here, the Y switch is connected to a first or second subnetwork of the redundant communication network via a first or second port, while the Y switch is directly connected or indirectly connected via a third port to the singly connected automation device. In addition, incoming data frames at the first, second and third ports are assigned to a first, second and third VLAN, respectively. In addition, the first and second ports are set up as untagged members for the first and third VLANs or for the second and third VLANs. The third port is set up as an untagged member for all three VLANs. Unicast MAC addresses learnt at the first two ports are automatically adopted as a static entry for the third VLAN. If a unicast MAC address learnt at the first two ports is deleted, the corresponding static entry for the third VLAN is also deleted.
DE 10 2011 082965 A1 discloses a method for operating a network arrangement comprising a plurality of network devices coupled to one another in a ring structure. Here, each network device has a control device and a switch device having at least two ports for coupling to a communication path. During operation, at least two VLANs are simultaneously provided in the ring structure. Here, a data packet is transmitted from the control device of a selected network device to one of the two VLANs via a port of the switch device. Here, the other port of the switch device of the selected network device is deactivated for the one VLAN. Redundant reliable transmission of data is possible through the use of two VLANs. Destabilization of the VLANs in the network ring is prevented by deliberately deactivating particular ports of the transmitting network device.
DE 10 2011 004064 A1 discloses an intermediate network in a ring topology for establishing a connection between two network domains, where the intermediate network comprises a first boundary node and a second boundary node that are boundary nodes of a first network domain. These boundary nodes are connected to one another via a first network connection within the first network domain. A third boundary node and a fourth boundary node that are boundary nodes of a second network domain are additionally provided. These boundary nodes are connected to one another via a second network connection within the second network domain. A first virtual network connection connects the first and third boundary nodes via an intermediate network. A second virtual network connection connects the second and fourth boundary nodes via the intermediate network. The first network connection, the second network connection, the first virtual network connection and the second virtual network connection have a ring topology in which a connection redundancy protocol is implemented.